The sintered diamond compact (which will be hereinafter referred to as "PCD") has been developed as a material for cutting tools of a long life time and has been in recent years widely used as an indispensable material for tools for machining the materials which are hard to work. The usage of PCD, however, is restricted to certain articles, because the production process thereof is too severe to produce a piece of PCD of a complicated configuration.
Particularly in the case of a drilling tool which is fabricated by fitting a blade tip of PCD in the groove of the top end of a shank and blazing the same thereto, PCD is hard to blaze on the shank, which is generally made of steel, together a substrate of a sintered alloy, etc. is bonded to a layer of PCD so that the blade tip is fixed to the shank by blazing the substrate to the shank.
With a blade tip of this type, however, the blazed surface is not very large so that it is not rigidly fixed to the shank. Accordingly, it has been earnestly required to provide a PCD sandwiched with a pair of substrates of sintered alloy, etc.
Further in preparing a tipped drill from a PCD blade tip having a substrate on only one surface thereof, it is necessary to fix a pair of blade tips precisely symmetrically to each other about the rotating center of the drill. But, with a PCD blade tip in which the PCD layer is sandwiched between a pair of substrates, such a complicated positioning of the blade tips is no longer necessary.
Although it has been earnesly required, it has been practically impossible to produce PCD blade tips of sandwich structure and thus such blade tips have not been seen in the market.